1. Field of the Invention
This invention relates to air-operated diaphragm spring brakes of the type used with air brake systems on vehicles such as trucks. In one of the aspects, the invention relates to an air-operated diaphragm spring brake wherein the spring-operated portion of the brake is prevented from operating off-center due to external forces biasing the pressure plate.
2. State of the Prior Art
Spring brake-applying actuators are in common use with air brake systems used on trucks, buses and towed vehicles. Such actuators normally include a service brake actuator for applying and releasing the brakes in response to delivery and exhaust of compressed air and a spring actuator disposed in tandem with the service brake actuator. The spring actuator uses spring force to operate the service brake actuator and apply brakes when the air in a spring actuator chamber is reduced below some predetermined level. Air may be reduced in the spring actuator to apply the brakes under the control of the operator or automatically as a result of failure of portions of the service brake air system.
In all such actuators, a barrel-shaped spring is used to store energy and to exert the large force required for braking in the event of air pressure failure. Air pressure acting on a movable wall is employed to compress the spring and maintain it in its brake release position. When the air is exhausted, the spring acts on the movable wall, typically a diaphragm or a piston, and through an actuating rod to exert the spring force on the service actuator to apply the brakes.
In service of the diaphragm brakes, the diaphragm can become misaligned with the springs, sometimes causing a binding of a spring-mounted pressure plate on the housing. In addition, misalignment may cause wear between the spring brake actuator and the guide therefor. This wear may cause leakage of pressure from the service brake actuator and spring brake actuator chambers.
It is thought that the misalignment is due to improper seating of the adaptor push rod on the diaphragm during compression and expansion of the spring brake spring. In the to Kurichh et al U.S. Pat. No. 3,926,094, issued Dec. 16, 1975, any lateral thrust of the spring is compensating by providing a pivotable joint between the spring actuating rod and the guide therefor, and also a pivotable joint between the actuating rod and the actuating rod plate which is in contact with the spring diaphragm. These features accommodate the lateral thrust of the spring to prevent wear between the spring actuating rod and the guide therefor. However, these features do not necessarily prevent dragging of the spring pressure plate on the housing. This problem is due to lateral shifting of the diaphragm with respect to the spring pressure plate. Lateral shifting of the diaphragm may be due to a whole host of problems including installation and brake adjustment problems.